Self-cleaning sieve device in containers for cellulosic pulp



March 1968 J. c. F. c. RICHTER 3,372,087

SELF-CLEANING SIEVE DEVICE IN CONTAINERS FOR CELLULOSIC PULP Filed April 20, 1964 4 Sheets-Sheet 1 INVENTOR. Jo/m/v C'FCT Fun/r51? /MZLA,MQ%ZZZM 770,6/VEV5 March 1968 J. c. F. c. RICHTER 3,

SELF-CLEANING SIEVE DEVICE IN CONTAINERS FOR CELLULOSIC PULP Filed April 20, 1964 4 Sheets-Sheet 2 INVENTOR. Jo/m/vCf/ T'CT Fla/175R BY W l na/4Q MM March 1968 J. c. F. c. RICHTER 3,

SELF-CLEANING SIEVE DEVICE IN CONTAINERS FOR CELLULOSIC PULP Filed April 20, 1964 4 Sheets-Sheet 5 I N VEN TOR.

March 1968 J. c. F. c. RICHTER 3, 7 ,087

' SELF-CLEANING SIEVE DEVICE IN CONTAINERS FOR CELLULOSIC PULP Filed April 20, 1964 4 Sheets-Sheet 4 IN VEN TOR.

United States Patent Ofilice 3,372,087 Patented Mar. 5, 1968 3,372,087 SELF-CLEANING STEVE DEVICE IN CONTAINERS FOR CELLULOSIC PULP Johan C. F. C. Richter, St.-Jean-Cap-Ferrat, France, assignor to Aktiebolaget Kamyr, Karlstad, Sweden, a company of Sweden Filed Apr. 20, 1964, Ser. No. 360,962 Claims priority, application Sweden, May 20, 1963, 5,556/ 63 7 Claims. (Cl. 162251) ABSTRACT OF THE DISCLOSURE There is provided an apparatus for deliquefying a pulp suspension in connection with a chemical treatment and/ or washing of the pulp, wherein sieve bodies are disposed in a container and the pulp suspension moves through the container in an axial direction. The sieve bodies are hollow and have sieve faces elongated in the direction of the pulp flow through which the liquid passes. The sieve bodies are moved in the direction of the pulp flow at substantially the same rate as the pulp flow whereby washing liquids and/ or treating chemicals move horizontally towards the sieve bodies and in a direction transverse to the pulp flow. After a predetermined movement of the sieve bodies, they are rapidly returned to their initial position whereby the rapid movement of the sieve bodies opposite to the direction of pulp flow removes fibers that have stuck to the sieve faces.

The present invention relates to a sieve device in an upright cylindrical container adapted for axially directed continuous feed of a suspension of a comminuted fibrous material, preferably cellulosic pulp, which container comprises hollow sieve bodies arranged within the container and distributed over its cross-section and having essentially vertical faces for separating-01f a part of the liquid contents from the pulp.

In sieve devices of said kind a difficulty consists therein that the movement of the pulp past the sieve faces of the sieve bodies often is too slow to keep the sieve faces clean, wherefore they are gradually clogged by fibers and require mechanical cleaning involving not-desired interruptions of the operation. In order to avoid said difliculty it has been proposed to put the sieve bodies in rotation, but said solution involves a disturbance of the desired axially directed flow of the pulp in the container.

According to the present invention the problem is solved in a fundamentally different manner, viz. by arranging the sieve bodies somewhat displaceable in the axial direction of the container, i.e. in the direction of flow of the pulp, so that they are free intermittently to accompany the pulp a small distance upwards in the axial direction of the container and to be brought back in the opposite direction. The return of the sieve bodies in the direction opposite to the flow direction of the pulp is preferably performed by a rapid movement, whereby fibers that may have stuck to the sieve, will loose their engagement with the sieve faces, whereas during the intervening longer time periods the sieve bodies are allowed to accompany the pulp in its slow motion in the axial direction. The sieve faces are thus maintained clean in a manner requiring merely comparatively simple means and a small amount of power.

The invention will be more closely described herein below with reference to the accompanying drawings. FIG. 1 is a vertical sectional view of a first embodiment, and FIG. 2 is a horizontal sectional view thereof taken along the line II in FIG. 1. FIG. 3 is a vertical sectional view of a second embodiment, FIG. 4 shows a detail on an enlarged scale, and FIG. 5 is a horizontal sectional view taken along the line V-V in FIG. 3.

In the drawings 11 designates the cylindrical wall of an upright container consisting of sheet iron or concrete and preferably adapted for the performance of any kind of chemical treatment of a suspension of cellulosic fiber material. Thus the container may be a digester for Wood chips, straw or similar cellulosic material, or a bleach tower for cellulosic pulp already digested and defibrated and of a more or less fluent consistency. The container may also be adapted merely for performing a washing operation of the pulp or effecting an increase of its consistency by separating-off a part of its liquid contents. The container is arranged to allow the flow of the fiber material in the upward direction, either fully continuously or semi-continuously, i.e. stepwise by periodically supplying thereto batches of pulp small in comparison to the volume of the container. Therefore the container is provided at its bottom with feeding devices (not shown) which cause the material to rise vertically up through the container. Provided at the upper end of the container is a device for discharging the material as it rises, through a side outlet 15. Said discharging device may consist of a scraper composed of obliquely set blades 17 carried by radial arms U attached to a rotary vertical shaft 21. Said shaft is arranged centrally in the container and its upper end is supported by a bearing 23 and driven by a motor 25 via a gear 27. If desired, the container could be closed at its upper end and held under a suitable super-atmospheric pressure.

The sieve arrangement essentially consists of two annular sieve bodies 29 and 31 which are concentric to each other and to the axis of the container and are located essentially at the same level. Either sieve body consists of two mainly cylindrical sieve plates 41, 43 of slightly different diameters which are put into each other and joined at their upper and lower edges. The distance between the sieve plates is considerably less than their axial extension and is chosen with regard thereto that the cavity formed between the sieve plates shall allow quite free flow of the liquid sieved-off and that the sieve body shall be of a sufiiciently resistant and rigid design. Thus, in any axial cross-section the sieve body is elongated in the vertical direction and has a pointed or rounded lower edge in order to offer the least possible resistance to movement in the axial direction relatively to the pulp. The sieve plates 41, 43 are essentially vertical and are provided with perforation apertures or vertically extending sieve slits distributed over essentially the entire surface. Preferably, however, at their lower parts the sieve bodies may be imperforate so that liquid sieved-off can be collected in the lower part of the cavities 47, 49 of the sieve bodies. The sieve bodies are located at such radial distances to the axis of the container that the sieving effect attained by them is comparatively evenly distributed over the cross-sectional area of the container.

The sieve bodies are rigidly attached to horizontally and radially directed supporting arms 44, 46, and 48, the

outer ends of which extend out through apertures 50 in the wall of the digester, said apertures being sufficiently long in the vertical direction to allow a restricted movement of said supporting arms in the axial direction of the container. Plates 51 attached to the supporting arms cover said apertures in order to restrictthe leakage therethrough. The supporting arms 44, 46, 48 are tubular and their cavities 52 are connected to the cavities 47 and 49 of the sieve bodies. The outer ends of said arms are connected by flexible hose sections 54 to an outer manifold 56 and a common outlet 58 for discharging such liquid as is separated off the pulp by means of the sieve bodies 29, 31.

According to the invention there is provided an operating device for displacing the sieve bodies vertically in one and/ or the other direction. In the embodiment shown in FIGS. 1 and 2 said operating device is located outside the container and is arranged to act upon the protruding ends of the supporting arms 44, 46, 48. For each supporting arm there is provided a hydraulic or pneumatic cylinder 60 having a vertically movable piston 62 therein which is connected to a fitting 66 surrounding the end of the supporting arm, e.g. 46, and slidably guided between rails 64. In operation, a pressure fluid is supplied simultaneously to the upper ends of the three cylinders 60 so that the supporting arms are moved uniformly downwards, thus displacing the sieve bodies rectilinearly and pushing their lower pointed edges down through the pulp. Due to the rapid movement of the sieve faces relatively to the pulp the latter rakes off such fibers as previously may have stuck in the sieve apertures. If desired, there may be inserted into the outlet 58 a valve which is closed simultaneously with said downward movement of the sieve bodies and which eliminates the pressure difference between the two sides of the sieve plates. This will further facilitate the release of particles stuck in the sieve faces so that the latter are disengaged from the pulp and can easily be brought to face a lower layer of the pulp. When the sieve bodies have been displaced to their lower limit, the pressure fluid is shut off, whereby the pistons are made free to move upwards. During the continued rise of the pulp in the container the pulp brings the sieve bodies with it upwardly on account of the friction between the pulp and the sieve faces, amplified by the pressure difference between opposite sides thereof. Therefore the withdrawal of the liquid takes place essentially without any relative movement between the pulp and the sieve bodies. Of course, the slow upward movement of the sieves effected by the rising pulp can be assisted by the hydraulic or pneumatic operating device. Thus for pulp consistencies corresponding to a dry content of to percent, it has proved to be advantageous to displace the sieves upwardly at a somewhat greater speed than that of the pulp. For instance, whereas in practice the rate of upflow of the pulp is of the order of 50 to 150 mm. per minute, the sieves should preferably be displaced upwardly at a rate of 75 to 200 mm. per minute. The downward movement of the sieves should be chosen considerably greater, e.g. 10 times greater.

The number of supporting arms can be varied, and merely one or a few of them need be made hollow in order to convey the separated liquid to the outside of the container. According to another modification the operating device is connected merely to one of the supporting arms.

In the case that the sieve device is meant to be used merely for withdrawing a part of the liquid contents of the fiber suspension from the solid fiber material, the device as above described is complete and operable. On the other hand, if the sieving operation shall take place without a simultaneous concentration of the pulp and in connection with an exchange of liquids, such as a partial or complete replacement of a treating liquid by a washing liquid or replacing the latter by a still cleaner washing liquid, means are also required for the supply of liquid.

In the embodiment shown in FIGS. 1 and 2, said means consist of essentially vertically extending spray tubes 68, 70 extending downwardly from the arms of the scraper 19, and of a spray aperture 72 located upon the extended lower end of the shaft 21. Washing liquid taken from a conduit 74 is supplied through connections in the shaft 21 and in the scraper arms to the spray tubes 68, 70 and the aperture 72. The ejection orifices of the spray tubes as well as the aperture 72 are located approximately at the level of the upper parts of the sieve bodies, so that the wash water and the liquid displaced thereby move essentially horizontally towards the sieve faces, i.e. in a direction transverse to the rising pulp, whereby the motion of the pulp is affected merely very slightly by the liquid flow therein. As shown in FIG. 2, the spray tubes 68, 70

are of a cross-section oblong or streamlined in the direction of their motion, whereby the power consumption of the driving motor 25 is held low and unnecessary agitation of the pulp is eliminated.

In the embodiment shown in FIGS. 3 to 5, the annular sieve bodies 29, 31 are carried by two radial supporting arms 75, 77, the outer ends of which are attached to the container wall 11 and the inner ends of which are attached to the hub 79 enclosing the rotary shaft 21 of the scraper 19. A pin 81 upon the shaft 21 moves in a groove 83 in the hub formed like one turn of a helical thread and a vertical step. When the shaft 21 is turned, the pin 81 cooperates with the upper border of the helical groove 83 in the hub, thereby raising the hub, the supporting arms 75, 77 and the sieve bodies 29, 31. The supporting arms are being elastically distorted and when the shaft 21 has turned almost one revolution so that the pin 81 reaches the vertical step of the groove 83, the tension of the supporting arms is released and said arms rapidly snap back to the lower end position, thereby pushing the sieve bodies a small distance down into the pulp.

The wash liquid is supplied by a number of nozzles 85 connected to separate supply tubes 87 located within the shaft 21 and within the arms 89 extending from the lower end of said shaft. A sieve girdle 91 is inserted in the container wall 11 at the level of the sieve bodies 29, 31. The rotary nozzles 85 are located at said level, too.

I claim:

1. An upright cylindrical container for axially directed feed of a suspension of a comminuted fiber material and having a sieve device therein, comprising hollow sieve bodies located within the container, distributed over its cross-secton and having essentially vertical sieve faces for withdrawal from the pulp of a part of its liquid contents, characterized in that the sieve bodies are somewhat movable in the axial direction of the container, so that they are free to accompany the pulp movement intermittently a small distance upwards in the axial direction of the container and at least one power operating means connected to the sieve bodies for axial movement thereof, whereby the sieve bodies are brought back in the opposite direction in order to facilitate the motion of the pulp past the sieve faces and to prevent the pulp from sticking to the same.

2. Device according to claim 1, characterized in that the sieve bodies are carried by supporting arms which extend radially and preferably horizontally and of which at least one arm projects through and is movable relatively to the wall of the container.

3. Device according to claim 1, in which the sieve bodies are carried at least partially by a shaft arranged centrally in the container and serving for rotating a scraper, characterized in that the vertical motion of the sieve bodies is derived from the rotary motion of said shaft relatively to the sieve bodies.

4. In an apparatus for treating a suspension of comminuted fiber material in a liquid medium, comprising a cylindrical container for accommodating an axial fiow of the suspension, a set of sieve bodies located within said container in a spaced relation to the cylindrical wall thereof, said sieve bodies having apertured walls extending essentially in the axial direction of said container, conduit means connected to said sieve bodies and extending to the outside of said container for discharging liquid medium having passed through said apertured walls, and means mounting said set of sieve bodies for positively displacing said set of sieve bodies axially in at least the directon opposite to the direction of flow of said suspension.

5. An apparatus as claimed in claim 4, further 'comprising: supporting means for said sieve bodies extending radially in the container and through the wall thereof, and pressure medium operated means located outside said container and cooperating with said supporting means for reciprocating said sieve bodies in the axial direction of the container.

6 6. Device according to claim 3 wherein the shaft also References Cited carries at least one spray tube.

7. Device according to claim 1 wherein the power UNITED STATES PATENTS operating means is located outside of the container and 1,061,767 5/1913 Stanley 162251 X is connected to at least one supporting arm for the sieve 5 1,607,013 11/ 1926 Mayerhofef 21O383 bodies, said power operating means being connected to an end of the supporting arm which projects through the DONALL SYLVESTER, Examinercontainer Wall. HOWARD R. CAINE, Examiner. 

